Method of and system for reducing static



Aug. 2 7, 1940.

METHOD P. M. HAFFCKE OF AND SYSTEM FOR REDUCING STATIC Filed April 19,1938 TONE FIlIER minim-0R P]: i lip M Hafyck e BY A TTORNE Y PatentedAug. 27, 1940 UNITED, STAT S (Granted under the act of March 3,[188 3,as amended April 30, 1928; 3'70 0. G. 757') This invention relates to amethod of and means for reducing interference with-the reception ofradio signals, by limiting the peaks of received signal waves when suchwaves have amplitudes in excess of a predetermined value.

Among the numerous are: it

To provide means responsive to excessive voltages on the plate of avacuum tube to by-pass such voltages to ground; i

To utilize a diodesection of certain dual pur-' pose tubes to by-passexcessive voltages asaforesaid; l

To provide a vacuum tube network whereb excessive surges of negativevoltages are vbypassed as aforesaid and the output wave is fiattenedwhile positive surges are flattened due to rectification by the signalgrid;

To provide in a vacuum tube network as next.

through "tubes as in Fig. 1 in cascade, with rectifying means across theinputsof two of thestages.

If the top of a radio wave is levelledoff the wave no longer remainsofpure sine form and will contain several harmonics ascomponents. Thisfact is the basis of the present method of static reduction and dependsupon the partial limiting of the peaks of the received waves in each ofseveral stages as the signal passes through and is amplified in thereceiver. z

The above effect is attained in a simple man ner, without a large numberof units of accessory equipment, by utilizing certain types of dualpurpose tubes as combined amplifiers and rectifiers, through theinsertion of a simple adaptor between the respective tubes and theirsockets, and certain other minor changes that will be apparent from thefollowing description.

Referring now-to Fig. 1, the vacuum tube 3 is of the type known to thetrade as 237 having an amplifier section that includes an anode 4,

a screen grid .5, suppressor grid 6 and control grid 1, the cathode 8being common to the above mentioned amplifier section and the diode:section that includes-the anode 9. The hook-up is largely conventionalexcept that a, capacitor Ill of large. capacity is. connected.betweenthe amplifier anode 4 and the diode anode 9. Thus,

METHOD OF AND SYSTEM Fon s'rATIo Philip M-tnafvfck, Washington, D. ,0. at Ap lication April 3 Serial NQ; 202,899 g 'IIJCIaimS. (01. 250

objects of this invention 1 PATENT R C N a 1..

when a heavy surge of received "energy causes the control grid 7 toswing hard toward the negative and thereby increases the plateresistance,

the rapid rise in voltage at anode 4 isby-passed through condenser ID tocathode 8 and thence to ground. This causesa flattening of the wave intheoutput circuit of the amplifier on the negative half of the inputcycle. On the other'half of the wave the signal grid swings stronglypos-.

tubes to, 3b and similar to the tube 3 in Fig.1

connected in cascade in a radio receiver. The tube 3a may be the firstintermediate frequency stage, the tube 32) the second intermediatefrequency and second detector combined and tube 30 maybe the first audiofrequency stage. The output anodes 4 of the tubes 3a, 3b and 3c arerespectively connected to the anode 9 of the diode section in each tubeby a large capacity condenser H], as in Fig.1. In addition, I haveprovided a double diode rectifier having one cathode 12 connected to thecontrol grid '1 of tube 30 and a cathode l3 connected to the controlgrid 1 of tube 3a, the two anodes I 4 of the tube H having a commonconnection through variable resistor I5 to ground. Thus. the tube IIwill become operative to by-pass the portions of waves in excess of apredetermined magnitude and initiate the generation of harmonics in theinput to the tube 3a and while the results will not be 100 per centperfect they willrbe increased in vtube3band still further in tube 30. Atone filter I6 is connected between tube 3b and the input to tube 30whereby the undesirable harmonies are rejected andkept outset the audiofrequency stage, the connection of cathode l3 oftube H to control gridof .tube 30. serving to surges are transferred to tube 3a, the signalgrid 1 of that tube and the cathode l2 and anode 14 of tube l l act as afull wave rectifier acrossthe input transformer and absorb the excessiveamplitudes of heavy static impulses,'bu-t due to the naturalcharacteristics of the voltage-current curve of such rectifiers, thereis aslight rise in the voltage drop across the rectifieruelements .asthe-current through therectifier increases and the efiective wave is notactually, brought down to a true flat-topped form, but is left roundedthough not nearly so high in proportion to the signal level asoriginally. The output of this stage thus contains a signal frequencyplus many harmonic components, which harmonic components are rejected bythe following tuned transformer. However, as all of the excess amplitudeis not thrown into harmonics tube 3b will also receive considerablesurge energy from the static and the diode section of tube 31) will,through its'connection to the anode 4 by capacitor It],

further reduce or flatten the output current Wave form.

The signal delivered to the tone filter therefore contains not onlysignal but also static which latter is now in large part audio harmonicsof the'signal tone frequency of such order that a much greaterpercentage, of such excessive surges of static are lost and thebackground and the inter-signal periods are largely devoid of highamplitude impulses. g

The resistor l5, when adjusted to have a low or even a zero value, maycause some lowering of the signal amplitude due to the loading action ofthe rectifyingelements, but even the heaviest static surges are alsoheld down to such an extent that although the signal is somewhat reducedthe noise of the heaviest static surges has been lowered toapproximately the same level as the signal. 30

The reception new sounds as though the static were only of signal levelinstead of many times as great. The hissing sound which is caused by theusual automatic volume control, and the persistant ringing of the audiotone filter and of the intermediate frequency stages, all of whichnecessitate a drastic reduction in the sensitivity, are

eliminated.

If a condenser be inserted in the lead of each of cathodes l2 and I3they will be thrown into parallel with the tuned input circuit of tube3a and will so change the circuit values of the input circuit that itwill be automatically'detuned with of any royalties thereon or therefor.

I claim: v

'1. A method of operating a pluralitylof dual purpose vacuum tubes incascade, each of which tubes has an amplifier section including a firstanode and a control grid, a diode section including a second anode, anda cathode common to both sections, comprising the steps of lay-passingto said second anode in each tube and thence to said cathode therein andto ground excessive voltages appearing on said first anode in such tubewhen a received impulse swings said control grid negative beyond apredetermined value, bypassing energy'ln each tube to ground as gridcurrent when the swing of said grid goes" positive beyond apredetermined value, by-passing to ground energy from the input 'of the:first of said tubes in proportion to the input amplitude in excess of apredetermined value, eliminating between the last of said tubes and thenext to last thereof undesired harmonics generatedgby bypassing currenttoflgroun-d as aforesaid; and bypassing to ground energy from the inputoisaid last tube in proportion to input amplitude above a predeterminedvalue to damp oscillations generated by the said elimination ofundesired harmonies.

2. A method of operating a plurality of dual purpose vacuum tubes incascade, each of which tubes has an amplifier section including a firstanode and a control grid, a diode section including a second anode, anda cathode common to both sections, comprising the steps of by-passing tosaid second anode ineach tube and thence to said cathode and groundexcessive voltages appearing on said first anode when a received impulseswings said-control grid negative beyond a predetermined value,by-passing to ground energy from the input of the first said tube inproportion to the input amplitude in excess of a determined value todamp oscillations generated by the said eliminationof undesiredharmonics. 3. A method of operating a plurality of dual purpose vacuumtubes in cascade, each of which tubes has an amplifier section includinga first anode and a control grid, a diode section including a secondanode, and a cathode'common to ,both sections, comprising the steps ofby-passing to-said second anode in each tube and thence to said cathodeand. ground excessive voltages appearing on said first anode when areceived impulse swings said control grid negative beyond apredetermined value above normal signal level only, by-passing energy ineach tube to ground as grid current when the swing'o'f said grid goespositive beyond a predetermined value, by-passing to ground energy fromthe-input of the first said tube in proportion to the input amplitude inexcess of a predetermined ,value, and by-passing energy from the inputof said last tube in proportion to input amplitude in said last tubeabove a predetermined value.

4. A method of operating aplur'ality of dual purpose vacuum tubes incascade, each of which tubes has an amplifier section including a firstanode and a control grid, a diode section including a second anode, anda cathode common to both sections, comprising the steps of by-passing tosaid second anodeuin. eacntube and thence to said cathode and groundexcessive voltages appearing on said first anode whenia received impulseswings said control grid negative-beyond a predetermined value abovenormal signal level only, by-passing to ground'energy from the in putsof the first and last said tubes in proportion to input amplitude inexcessof a predetermined value. 1

5. A method of operating a plurality of dual purpose vacuum tubes incascade, each of which,

tubes has an amplifier sectionincluding afirst anode and a control grid,:a diode section including a second anode, and a cathode common to bothsections, comprising the steps of by-passing to said second anode ineach tube and thence to said cathode and ground excessive voltagesappearing on said first anode when a received impulse swings saidcontrol grid negative beyond a predetermined value abovenormal signallevel i amplitude in excess of a predetermined value.

6. A method of operating a plurality of dual purpose vacuum tubes incascade, each of which tubes has an amplifier section including a firstanode and a control grid, a diode section including a second anode, anda cathode common to both sections, comprising the steps of by-passing tosaid second anode in each tube and thence to said cathode and groundexcessive voltages appearing on said first anode when a received impulseswings said control grid negative beyond a predetermined value abovenormal signal level only, and by-passing energy in each tube to groundas grid current when the swing of said grid goes positive beyond apredetermined value.

7. A method of operating a dual purpose vacuum tube having an amplifiersection including a first anode and a control grid, a diode sectionhaving a second anode, and a cathode common 'to both sections,comprising the steps of bypassing to said second anode and thence tosaid cathode and ground excessive voltages appearing on said first anodewhen a received impulse swings said control grid negative beyond apredetermined value above normal signal level only, and by-passingenergy to ground as grid current when the swing of said grid goespositive beyond a predetermined value.

8. A method of operating a dual purpose vacuum tube having an amplifiersection including a first anode and a control grid, adiode sectionhaving a second anode, and a cathode common to both sections, comprisingthe step of by-passing to said second anode and thence to said cathodeand ground excessive voltages appearing on said first anode when areceived impulse swings said control grid negative beyond apredetermined value above normal signal level only.

9. In radio receiving apparatus, a plurality of dual purpose vacuumtubes connected in cascade, each of said tubes having a cathode, a firstanode adjacent said cathode, a control grid and an output anode;capacitive means connecting each said first anode with the output anodein the same tube, a tone filter in the output of the next to last ofsaid tubes, rectifying means comprising a cathode connected to thecontrol grid of the first of said tubes and an anode, rectifying meanscomprising a cathode connected to the control grid of the last of saidtubes and an anode, and common Variable resistive means connecting boththe anodes of said rectifying means to ground.

10. In radio receiving apparatus, a plurality of dual purpose vacuumtubes connected in cascade, each of said tubes having a cathode, a firstanode adjacent said cathode, a control grid and an output anode;capacitive means connecting each said first anode with the output anodein the same tube, rectifying means comprising a cathode connected to thecontrol grid of the first of said tubes, and an anode rectifying meanscomprising a cathode connected to the control grid of the last of saidtubes and an anode, and common variable resistive means connecting boththe anodes of said rectifying means to ground.

11. In radio receiving apparatus, a plurality of dual purpose vacuumtubes connected in cascade, each of said tubes having a cathode, a firstanode adjacent said cathode, a control grid and an output anode, anoutput circuit connected to each said output anode and capacitive meansconnecting each said first anode with the output anode in the same tubeto by-pass excessive energy surges from said output circuit to saidfirst anode when said control grid is swung excessively negative.

12. A vacuum tube network, comprising a dual purpose vacuum tube havingan amplifier sec' tion including an anode and a control grid, a diodesection including an anode, and a cathode common to both sections, meansto transfer from the first mentioned anode to the second mentioned anodealternating voltages in excess of a predetermined value and output meansindependent of said transfer means connected to said amplifier sectionanode.

13. In radio receiving apparatus, a plurality of dual purpose vacuumtubes each having an amplifying section including an anode and a controlgrid, a diode section including an anode, and

a cathode common to both said sections, means to transfer from the anodein said amplifying section to the anode in the diode section alternatingvoltages in excess of a predetermined value and output means independentof said transfer means connected to said amplifier section anode.

14. A method of operating a dual purpose Vacuum tube having an amplifiersection including a first anode and a control grid, a diode sectionhaving a second anode, and a cathode common to both sections, comprisingthe steps of by-passing to said second anode and thence to said cathodeand ground excessive voltages appearing on said first anode when areceived impulse swings said control grid negative beyond apredetermined value, icy-passing energy to ground as grid current whenthe swing of said grid goes positive beyond a predetermined value andtaking off the output energy in a conventional manner.

PHILIP M. I-ILAFFCKE.

